Synthesis and characterization of polyurethane foams derived of fully renewable polyester polyols from sorbitol

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This work globally redesigns the conventional approach in obtaining polyurethane foams (PUF), from sorbitol. Fully biobased polyester polyols were synthesized from sorbitol, adipic or succinic acid and different renewable C2 to C12 diols as the first step towards the elaboration of PUF. Sorbitol-based polyester polyols were synthesized through a two-step esterification without catalyst. The absence of a catalyst limits some side reactions and focuses the reaction on the primary hydroxyl groups of the sorbitol, to obtain the linear molecular structure. The global yields of the corresponding esterifications were above 80%. Hydroxyl values and acid values of the corresponding linear biobased polyester polyols ranged from 440 to 683 mg KOH/g, and from 11 to 49 mg KOH/g, respectively. Acid values were decreased below 10 mg KOH/g by neutralization. PUF were prepared with polyols blends containing this biobased polyester polyol (up to 75wt%) and a conventional fossil based polyol e.g., oxypropylated glycerol, which present a high fossil content. The final biobased content of the PUF ranged up to 28wt% in contrast to 9wt% for the reference. Then the addition of neat glycerol to the polyol blend increased the final biobased contents of the PUF foams up to 31wt%. In contrast with the traditional approach consisting of modifying the catalyst content, the activation of the reactive foaming process was improved through initial polyols blends. The final biobased PUF foaming kinetic was similar to that of the polyether polyol, used as a reference. Finally, the effects of chemical and physical blowing agents (water vs. isopentane) were compared on the foaming rate and foam structure. The use of chemical blowing agent efficiently decreased the foam gel time of 33% and increased the foaming rate of 1mm/s with biobased systems. Besides, the polyols architecture has a strong influence on the foam tack free time which varied from 50 to 235s for the studied PUF.